NGC 869 and NGC 884

	h Persei, NGC 869	chi Persei, NGC 884
Right Ascension	2 : 19.0 (h:m)	2 : 22.4 (h:m)
Declination	+57 : 09 (deg:m)	+57 : 07 (deg:m)
Distance	7.1 (kly)	7.4 (kly)
Visual Brightness	4.3 (mag)	4.4 (mag)
Apparent Dimension	30 (arc min)	30 (arc min)

Perhaps known pre-historically. Cataloged 130 B.C. by Hipparcos.

The famous double cluster in Perseus was known in antique times (probably even pre-historically), and first cataloged by the Greek astronomer Hipparcos.

Both clusters are situated in the Perseus OB 1 association, and also only a few hundred light-years appart, at a distance of over 7000 light years. They are both quite young: h is listed at 5.6, chi at 3.2 million years (Sky Catalog 2000); their hottest main sequence stars are of spectral type B0. They are approaching us at 22 (h) and 21 (chi) km/sec, respectively.

O'Meara and Green (2003) point out to some historical confusion about the identity of the designations or names, or the objects "Chi" and "h" Persei. As they point out, since the 1840s, the name "Chi" is attributed to NGC 884, and "h" to NGC 869. However, these authors point out that very probably, Tycho Brahe measured one position for the "nebulous star" that is actually the double cluster, and Johann Bayer designated this "star" as Chi. Probably, he used the name "h Persei" for a fainter nearby star.

Both clusters are listed in the SAC 110 best NGC object list. The double cluster is in the RASC's Finest N.G.C. Objects Objects list. It is Caldwell 14 in Patrick Moore's list.

NGC Online data for NGC 884

References

• Stephen James O'Meara and Daniel W.E. Green, 2003. The Mystery of the Double Cluster. Sky and Telescope, Vol. 105, No. 2, p. 116-119 (Februaty 2003)

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Hartmut Frommert
Christine Kronberg
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Last Modification: July 2, 1998